Hepatitis C (HCV) is a small enveloped, positive stranded RNA virus that represents a major health burden worldwide with more than 170 million individuals currently infected [Thomson, B. J. and R. G. Finch, Hepatitis C virus infection. Clin Microbiol Infect, 2005. 11(2): p. 86-94]. One of the most successful of all human viruses, HCV preferentially infects heptocytes and is able to persist in the livers of up to 70% of all infected individuals [Bowen, D. G. and C. M. Walker, Adaptive immune responses in acute and chronic hepatitis C virus infection. Nature, 2005. 436(7053): p. 946-52]. It is estimated that up to 30% of chronically infected individuals will develop progressive liver disease, including cirrhosis and heptocellular carcinoma (HCC) during their lifetime making HCV infection the leading causes of liver transplantation in the world. In addition, HCV and HBV infections are implicated in 70% of all cases of HCC, which is the third leading cause of cancer deaths worldwide [Levrero, M., Viral hepatitis and liver cancer: the case of hepatitis C. Oncogene, 2006. 25(27): p. 3834-47].
Due to the persistent nature of the virus, HCV infection can be extremely difficult and expensive to treat. Most infected individuals do not receive treatment. However, those that do, pay on average $17,700 to 22,000 US for standard treatment protocols [Salomon, J. A., et al., Cost-effectiveness of treatment for chronic hepatitis C infection in an evolving patient population. Jama, 2003. 290(2): p. 228-37]. Genotype 1 infection, the most prevalent in Europe and North America, has the poorest prognosis with as little as 42% of individuals responding to standard treatments [Manns, M. P., et al., Peginterferon alfa-2b plus ribavirin compared with interferon alfa-2b plus ribavirin for initial treatment of chronic hepatitis C: a randomised trial. Lancet, 2001. 358(9286): p. 958-65].
Therefore, the high prevalence of infection, lack of effective treatments and economic burden of chronic HCV, illustrates the urgent need for the development of novel immune therapy strategies to combat this disease. Currently there is no prophylactic or therapeutic vaccine for HCV.
Understanding the adaptive immunity to this virus is critical for designing strategies, such as DNA vaccines, to combat viral infection. Although virus-specific antibodies are detected within 7-8 weeks post HCV infection [Pawlotsky, J. M., Diagnostic tests for hepatitis C. J Hepatol, 1999. 31 Suppl 1: p. 71-9] they do not protect against reinfection [Farci, P., et al., Lack of protective immunity against reinfection with hepatitis C virus. Science, 1992. 258(5079): p. 135-40; Lai, M. E., et al., Hepatitis C virus in multiple episodes of acute hepatitis in polytransfused thalassaemic children. Lancet, 1994. 343(8894): p. 388-90] and can be completely absent following the resolution of infection [Cooper, S., et al., Analysis of a successful immune response against hepatitis C virus. Immunity, 1999. 10(4): p. 439-49; Post, J. J., et al., Clearance of hepatitis C viremia associated with cellular immunity in the absence of seroconversion in the hepatitis C incidence and transmission in prisons study cohort. J Infect Dis, 2004. 189(10): p. 1846-55].
Thus, one of the major challenges in vaccine development for HCV is that unlike other hepatitis viruses, such as Hepatitis A and Hepatitis B, where successful antibody-based vaccines have been created, protection against HCV infection does not appear to be antibody mediated. Although the exact correlates of immune protection remain to be elucidated, numerous studies of both acutely infected patients and chimpanzees, have provided compelling evidence that strong T helper 1 (Th1) responses directed against the more genetically conserved non-structural regions of the virus are associated with clearance of HCV infection. See Missale, G., et al., Different clinical behaviors of acute hepatitis C virus infection are associated with different vigor of the anti-viral cell-mediated immune response. J Clin Invest, 1996. 98(3): p. 706-14; and Diepolder, H. M., et al., Possible mechanism involving T-lymphocyte response to non-structural protein 3 in viral clearance in acute hepatitis C virus infection. Lancet, 1995. 346(8981): p. 1006-7. Also, importantly, it has been shown that localization of HCV-specific T cells to the liver rather than peripheral blood is critical for both reduction in viral load and clearance of acute infection. See Thimme, R., et al., Determinants of viral clearance and persistence during acute hepatitis C virus infection. J Exp Med, 2001. 194(10): p. 1395-406; and Shoukry, N. H., et al., Memory CD8+ T cells are required for protection from persistent hepatitis C virus infection. J Exp Med, 2003. 197(12): p. 1645-55
Furthermore, it appears that infected individuals that mount an early, multi-specific, intrahepatic CD4+ helper and CD8+ cytotoxic T-cell response tend to show elimination of HCV infection [Lechner, F., et al., Analysis of successful immune responses in persons infected with hepatitis C virus. J Exp Med, 2000. 191(9): p. 1499-512; Gerlach, J. T., et al., Recurrence of hepatitis C virus after loss of virus-specific CD4(+) T-cell response in acute hepatitis C. Gastroenterology, 1999. 117(4): p. 933-41; Thimme, R., et al., Determinants of viral clearance and persistence during acute hepatitis C virus infection. J Exp Med, 2001. 194(10): p. 1395-406; Grakoui, A., et al., HCV persistence and immune evasion in the absence of memory T cell help. Science, 2003. 302(5645): p. 659-62].
DNA vaccines have many conceptual advantages over more traditional vaccination methods, such as live attenuated viruses and recombinant protein-based vaccines. DNA vaccines are safe, stable, easily produced, and well tolerated in humans with preclinical trials indicating little evidence of plasmid integration [Martin, T., et al., Plasmid DNA malaria vaccine: the potential for genomic integration after intramuscular injection. Hum Gene Ther, 1999. 10(5): p. 759-68; Nichols, W. W., et al., Potential DNA vaccine integration into host cell genome. Ann N Y Acad Sci, 1995. 772: p. 30-9]. In addition, DNA vaccines are well suited for repeated administration due to the fact that efficacy of the vaccine is not influenced by pre-existing antibody titers to the vector [Chattergoon, M., J. Boyer, and D. B. Weiner, Genetic immunization: a new era in vaccines and immune therapeutics. FASEB J, 1997. 11(10): p. 753-63]. However, one major obstacle for the clinical adoption of DNA vaccines has been a decrease in the platforms immunogenicity when moving to larger animals [Liu, M. A. and J. B. Ulmer, Human clinical trials of plasmid DNA vaccines. Adv Genet, 2005. 55: p. 25-40]. Recent technological advances in the engineering of DNA vaccine immunogen, such has codon optimization, RNA optimization and the addition of immunoglobulin leader sequences have improved expression and immunogenicity of DNA vaccines [Andre, S., et al., Increased immune response elicited by DNA vaccination with a synthetic gp120 sequence with optimized codon usage. J Virol, 1998. 72(2): p. 1497-503; Deml, L., et al., Multiple effects of codon usage optimization on expression and immunogenicity of DNA candidate vaccines encoding the human immunodeficiency virus type 1 Gag protein. J Virol, 2001. 75(22): p. 10991-1001; Laddy, D. J., et al., Immunogenicity of novel consensus-based DNA vaccines against avian influenza. Vaccine, 2007. 25(16): p. 2984-9; Frelin, L., et al., Codon optimization and mRNA amplification effectively enhances the immunogenicity of the hepatitis C virus nonstructural 3/4A gene. Gene Ther, 2004. 11(6): p. 522-33], as well as, recently developed technology in plasmid delivery systems such as electroporation [Hirao, L. A., et al., Intradermal/subcutaneous immunization by electroporation improves plasmid vaccine delivery and potency in pigs and rhesus macaques. Vaccine, 2008. 26(3): p. 440-8; Luckay, A., et al., Effect of plasmid DNA vaccine design and in vivo electroporation on the resulting vaccine-specific immune responses in rhesus macaques. J Virol, 2007. 81(10): p. 5257-69; Ahlen, G., et al., In vivo electroporation enhances the immunogenicity of hepatitis C virus nonstructural 3/4A DNA by increased local DNA uptake, protein expression, inflammation, and infiltration of CD3+ T cells. J Immunol, 2007. 179(7): p. 4741-53]. In addition, studies have suggested that the use of consensus immunogens may be able to increase the breadth of the cellular immune response as compared to native antigens alone [Yan., J., et al., Enhanced cellular immune responses elicited by an engineered HIV-1 subtype B consensus-based envelope DNA vaccine. Mol Ther, 2007. 15(2): p. 411-21; Rolland, M., et al., Reconstruction and function of ancestral center-of-tree human immunodeficiency virus type 1 proteins. J Virol, 2007. 81(16): p. 8507-14].
DNA vaccines encoding HCV NS3 and NS4 are disclosed in Lang, K. A. et al. Vaccine vol 26, issue 49, pp 6225-6231 (November 2008).
Therefere, there still remains a need for an effective vaccine against HCV. Also, there still remains a need for effective methods of treating individuals infected with HCV.